The invention is directed to lockable cartons, more specifically to lockable cartons formed from two half sections which are foldable onto one another, and which can be releasably locked together. One of the carton sections is formed with one or more compartments, with the second section forming the carton cover.
There are many types of lockable cartons which have been designed and used for storing many types of products, e.g., perishable food cartons. Depending upon the type of food the carton is designed to hold the base is formed with one or more compartments. Egg cartons are designed with the base formed with rows of multiple egg compartments, while those designed for hamburgers or sandwiches include a base having one or more compartments for receiving the sandwich and accompanying salads.
The carton cover may either be separate or integrally connected along one side to the base portion. The latter type of covers are designed to be folded over and temporarily locked to the base portion. Typically, either the cover or base is formed with a latch which can clasp a portion of the other carton section. This latch is designed to allow the two sections to be releasably held together.
Generally, food cartons are manufactured from either wood pulp or a thermoformed plastic. Wood pulp cartons are generally more rigid, while thermoformed plastic cartons provide a degree of thermal insulation and are particularly useful for hot and cold foods. However, one particular disadvantage with thermoformed plastic cartons results from the method of manufacturing the carton. If during the forming process the plastic is stretched it may become weakened at the stretched portion. Since thermoformed cartons are typically formed by pressing a plastic sheet between two heated mold platens the possibility of stretching the plastic sheet is dependent upon the design of the carton.
This potential weakening of a stretched portion of the plastic is particularly critical if the stretching occurs in the locking latches. The integrity of the locking latches is critical in order to provide a reliable clasping of the carton sections together. For certain applications it is desirable to extend the locking latches upwards from the carton half. This better positions the locking latch to clasp onto the oppposing carton half. However, in order to avoid the problems associated with stretching the plastic during the thermoforming process, the carton latches are typically not formed as independent structures, but are formed as part of a flap which extends out along the length of the carton side.
Examples of cartons which are designed to avoid stretching the plastic by forming one or more latches as a flap are disclosed in U.S. Pat. Nos. 4,612,153; 4,625,905; 4,625,906; and 4,625,907, all of which were issued to Raj K. Mangla and assigned to Mobile Oil Corporation. These patents also discuss the disadvantages associated with stretching the plastic, and primarily in forming the locking latches.